Chlamydia trachomatic (Ct) is one of the most common sexually transmitted pathogens. Cervicitis is central to the epidemiology and pathogenesis of other Ct syndromes. A model of cervicitis has been developed in the outbred CF-1 mouse (and other inbred strains) using a human oculogenital isolate of Ct. The specific aims are to: (1) study the host immunologic response to infection in progesterone treated and unmanipulated animals; (2) characterize the immunologic requirements for protection induced by immunization; and (3) expand the model by utilizing other Ct isolates of differing serovars and determining whether there is heterologous protection. The immune response to infection will be studied in progesterone treated and hormonally unmanipulated animals by examining the serologic, both genital and systemic, and cell-mediated immune responses by enzyme-immunoassay and lymphocyte-proliferation assay. B-cell deficient CBA/N and T-cell deficient nu/nu mice will be infected along with their sufficient counterparts to determine the roles of both arms of the immune system in this infection. The immunology of protection after prior infection and after immunization will be studied, using the same assays and congenic murine strain. In addition, it will be determined whether immune antibody can neutralize Ct in vitro or protect animals after passive administration. Finally, the model will be expanded using other Ct serovars (D,I) with the aim of determining whether heterologous protection can be conferred. Our long term goals are to better understand the immunologic response to genital Ct infection and the factor(s) responsible for its termination or progression. Finally we wish to study the mechanism by which immunization induces protection in the hopes that an effective vaccine may someday be developed.